1. Field of the Invention
The invention relates to a heatable fluid line having at least one pipeline and at least one electrical heat conductor extending at least over a partial section of the length of the pipeline. The present invention furthermore relates to a method for producing an assembled fluid line of this kind and the use thereof.
2. Related Technology
The term “assembling” or “assembly” of the line as used herein with the present invention is understood to mean the final stage of manufacture of the ready-to-install fluid line, after which the line can be delivered as a fully equipped component—for, example, according to customer specifications—provided with connector parts, such as fluid coupling parts and/or line connectors, and is ready for industrial use, preferably in the motor vehicle industry.
Heatable fluid lines in various formats are known and used, for example, in fluid distribution systems of motor vehicles. The fluid can be, for example, water for a windshield washing system or an aqueous urea solution, like the one used for reduction of nitrogen oxides in exhaust SCR catalysts (SCR=Selective Catalytic Reduction). The liquid can freeze at low ambient temperatures. Fluid feeding elements, such as pumps or hoses, are therefore heated in order to prevent freezing or in order to thaw an already frozen fluid. In order to achieve this, the heatable components within the fluid system are connected via fluid lines, wherein the latter can also be electrically heated.
High demands, which are a result of the operating conditions, are placed on the heatable fluid lines in the mentioned systems. These demands especially concern the possible occurrence of high temperatures, which at certain points of the system and/or of the lines can be as high as 140° C. to 180° C., for example, and briefly also even as high as 200° C., and in addition the occurrence of high absolute pressures, which are usually within the range of 5 bar to 10 bar, sometimes also within the range of up to 15 bar, the occurrence of pressure pulses that have to be compensated, and even the occurrence of changes in volume, which are associated, for example, with the freezing under freezing conditions and subsequent thawing of the fluid. With respect to the stress variable, it can be spoken here of a so-called ice pressure resistance of the line.
A differentiation between an adaptive, either external or internal, bonding and an integrated bonding of basic embodiment variants can be made in heatable fluid lines with respect to the bonding of the heat conductor to the pipeline.
An adaptive connection, in which the heat conductor rests on the outer side of the pipeline, is described in EP 1 985 908 A1. This document relates to a line connector for media lines comprising, on the one hand, a connection piece configured with at least one terminal portion for terminal connection to a fluid line of the kind described above or configured with an assembly, and having, on the other hand, a transition portion adjacent to the terminal portions provided with a flow channel. In the region of the transition portion are provided electric heating means in an arrangement that at least partially encloses the flow channel. Problems occur with regard to the freezing resistance of the fluid line and also a limited high temperature suitability or thermal resilience during use of a pipeline made from one of the normally utilized plastic materials. The resilience of the heat conductor, usually configured as wire braid, furthermore depends from the geometry of the pipeline; the result is an increased connection expense, and the fact that pulsations cannot be sufficiently compensated.
An additional known adaptive connection, in which the heat conductor rests however in the interior of the pipeline, is described in EP 2 040 510 A1. Problems occur herein again with regard to a limited freezing resistance and high temperature characteristics and/or long-term thermal resilience and also with regard to insufficient compensation of pulsation when a standard plastic is used as material for a pipeline of the kind described above. An additional disadvantage is the absence of pipe insulation, so that the fluid line is not suitable for low temperatures within the range of less than −15° C.
Known heatable fluid lines of the kind described above with fully integrated heat conductor and pipeline are also described in DE 10 2006 051 413 A1 and DE 102 01 920 A1.
The first document relates to an electrically heatable fluid line having an interior cross sectional region enclosing a medium feeding channel, a heat conductor arrangement arranged in heat conducting connection with the interior cross sectional region, and an external cross sectional region surrounding the heat conductor arrangement. A spacer layer, which separates the heat conductor arrangement from the external cross sectional region and has a lesser mechanical stability than the interior cross sectional region and the external cross sectional region, is provided between the interior cross sectional region and the external cross sectional region. It is consequently possible to bisect the external cross sectional region and to pull it off the end of the fluid line without damaging the heat conductor.
Because the spacer layer has a comparatively lesser mechanical stability, it can also be readily removed, and specifically manually. But this known fluid line also has the problems of limited freezing resistance and a limited high temperature suitability and/or thermal resilience when used as a pipeline in which the internal and/or external cross sectional region of the pipeline is made of a technical grade plastic. A greater consumption of material is moreover required because of the multiple layer wall structure. A greater effort is required during assembly to expose the heat conductor—and thus also a greater connection effort—in comparison to the adaptive connections of heat conductor and pipeline. And in addition, an insufficient pipe insulation and a deficient pulsation compensation are disadvantages, as is also the difficulty to realize connection variants of the fluid line.
The second document relates to a flexible multilayer heatable hose with at least one reinforcing layer and one elastomeric outer layer, and also with an electric heat conductor used to heat a medium flowing in the hose. This hose is likewise to be considered as a—flexible—pipeline of the kind described above. The heat conductor extends at least over a partial section of the length of the hose and consists of a metallic core and a casing. The heat conductor is embedded outside of the outer ply of the reinforcing layer, but under or within the outer elastomer layer, and can be exposed by a radially outward acting force in order to bisect the original or weakened outer elastomer layer, but without damaging its metallic core and its casing, and can be electrically connected directly to an electrical plug connector. In this known hose there are problems with regard to the large amount of material required to ensure a sufficient wall strength, the limited potential to form variants, the deficient pipe insulation and comparatively high connection expense.